1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method and, more specifically, to an image processing apparatus and an image processing method which perform image processing for drawing information including image information and color correction information.
2. Description of the Related Art
In general, in a conventional image forming apparatus such as a printer apparatus which performs image formation on the basis of color image data input from an information processing apparatus such as various client computers, an image is formed by using color materials of cyan (C), magenta (M), yellow (Y), and black (K).
On the other hand, when a document is formed by the image processing apparatus, a display device such as a CRT display or a liquid crystal display is used. For this reason, a variety of image processing is performed with the information processing apparatus by using R (red), G (green), and B (blue) values which are color components displayed the display device. Color image data expressed by R, G, and B values obtained as a result of the image processing are frequently sent to the image forming apparatus.
In this case, in the image forming apparatus, after the R, G, and B values are converted into C, M, Y, and K values, image formation is performed by using the C, M, Y, and K values. However, achromatic characters or the like which actually should be printed with a monochromatic K-color material (image formation) are printed with a color mixture of the color materials of C, M, Y, and K. The characters or the like may then disadvantageously blur or fade.
To this problem, the following technique is known conventionally. That is, intermediate images described per each object by analyzing a color image input from a host computer are generated, and the intermediate images are converted into a YMCK image in which, the color is regarded as gray to set the components other than the K component are set to 0 (zero) when R value=G value=B value for intermediate color data images (for example, see Japanese Patent Application Laid-Open (JP-A) No. 9-27915).
To solve the above problem, the following technique is also known. That is, it is determined whether all R, G, and B values of each pixel of color image data in an RGB color space input from a host computer are 0 (zero). Pixels in which all the values are zero are determined to be a black character, and the pixels are formed with only black recording material (for example, see Japanese Patent Publication No. 3359070).
In recent years, the frequency of adding color correction information for color image data for display devices or the like has increased in operating systems and application programs of client computers (simply “applications” hereinafter). More specifically, in many cases, the frequency has increased of sending color image data with added color correction information independent on devices, not the R, G, and B values themselves, to an image forming apparatus.
In this case, when only comparison of color component values is performed as in the techniques disclosed in JP-A No. 9-27915 and Japanese Patent Publication No. 3359070, it is difficult to determine whether an image has an achromatic color to which a K color material of a single color must be applied. In these techniques, an erroneous determination is easily made. When an erroneous determination is made, image forming cannot be performed with accurate colors.
More specifically, when color image data to which color correction information is not added and to which an RGB color space is applied is input, it can be easily determined whether an image has an achromatic color (gray) by checking whether the condition R value=G value=B value is satisfied. However, when the color correction information is added, even though the condition: A value=B value=C value is satisfied where A, B, and C are input values of three-color components, an image does not always have achromatic color. In order to know the colors of the image, the color correction information must be referred to.
For example, for typical drawing information formed to include color correction information and color image data, the page description language PostScript is cited. In PostScript, a color space and values of respective color components are set before an object is drawn in order to perform color setting. For example, when a color component value (0, 0, 0) is designated in the RGB color space, a description as in the example shown in FIG. 11 is obtained.
When the color correction information is added, a description as in the example shown in FIG. 12 is obtained. The portion from ‘[/CIEBasedABC<<’ as far as ‘>>]setcolorspace’ is a region corresponding to the color correction information, which includes a large number of items such as define statements and parameters, and has a very complex structure. In addition, depending on the applications, as in the example shown in FIG. 13, a more complex description may be required, with description contents often varying with each application.
As a method of determining whether the color is to be replaced with a single color, i.e., black, with having referred to the color correction information when the color correction information is added, the following method is considered. That is, a large number of combinations of items of color correction information and color component values, by which achromatic color is set as a result, are stored as standard patterns in advance. Pattern matching between the standard patterns and input color image data with the color correction information is then performed to make the determination. However, this method can be used with only a few applications, limiting the scope of application.
The above problems arise not only when an applied color material is a single-color material K but also when another single-color material (one of color materials C, M, and Y) is employed.